Preparation of unsaturated ethers



Patented Aug. 16, 1949 PREPARATION OF UNSATURATED ETHERS William F. Gresham, Wilmington, Del., assignor to E. I. du Pont de Nemours Accompany, Wilmington, Del., a corporation of Delaware No Drawing. Application June 5, 1947, Serial No. 752,845

' 11 Claims. (01. 260-615) This invention relates to the synthesis of 1,2- dialkoxyethylenes, and more particularly a method for the preparation of 1,2-dimethoxyethylene, which is a novel composition of matter.

In the copending application of W. F; Gresham and R. E. Brooks, S. N. 680,072, filed June28, 1946, now Patent No. 2,449,470, it is disclosed that 1,1,2-trialkoxyethanes can be prepared by reacting a dialkyl formal with carbon monoxide and hydrogen in the presence of an alkanol at a temperature within the range of 100 to350 C. under a pressure of at least atmospheres in the presence of a nickel-containing or cobalt-containing catalyst.

An object of the present invention is to prepare 1,2-dialkoxyethylenes. Another object of the invention is to provide a process for preparing 1,2-dialkoxyethylenes from the 1,1,2-trialkoxyethanes which may be prepared as disclosed in the said copending application, S. N. 680,072. Other objects of the invention will appear hereinafter.

It has been discovered in accordance with this invention that 1,2-dialkoxyethylenes can be prepared by pyrolysis of 1,1,2-trialkoxyethanes. For example, it has been discovered that 1,2-dimethoxyethylene can be prepared in excellent yield by heating 1,1,2-trimethoxyethane at elevated temperature, whereby demethanolation occurs, preferably in the presence of a catalyst, ashereinafter described. 'Moreover, 1,1,2 -tria1koxyethanes containing inert substituents can also be pyrolyzed in a similar manner; e. g., the pyrolysis of CH3OCH2CHOCH3CH(OCH3) 2 yields a mixture of CH3OCI-I2-COCH3=CHOCH3+CH3OH.

The 1,1,2-trialkoxyethanes which may be em- \ployed in the practice of this invention include 1,1,2 trimethoxyethane, 1,1,2 triethoxyethane, 1,1,2-tributoxyethane, etc. The pyrolysis of these substances to the corresponding dialkoxyethylene takes place preferably, but not necessarily, in the vapor phase. Good results are obtained in vapor phase operation at a temperature within the range of about 300 to 450 C., preferably about 350 to 375 C. Much lower temperatures may be employed, however, especially when the pyrolysis of the 1,1,2-trialkoxyethane is carried out in the liquid phase, e. g. in the presence of a sodium-ah bodiments. An outstanding catalyst is barium hydroxide-silica gel, which may :be prepared by impregnating silica gel with aqueous barium hydroxide solution and thereafter removing the Water from the resulting mixture. Other effective catalysts include boron phosphate, aluminum oxide, titania gel, aluminum phosphate, silica gel, alkali metal carbonate-silica gel and acidic claylike materials of the kind commonly employed in cracking petroleum. The catalyst is employed preferably in granular form but may also be employed in the form of a very finely divided solid, which, in certain embodiments, may be suspended in the reaction vessel in the manner commonly used in processes employing the fluidized solid catalyst technique.

The invention is illustrated further by means of the following examples.

Example 1.-1,1,2-trimethoxyethane vapor was passed over a barium hydroxide-silica gel catalyst at a space velocity of 200 at a temperature of about 350 C. The resulting product was condensed and thereafter distilled through an emcient fractionating column. After removal of a methanol-dimethoxyethylene azeotrope the distillation temperature rose rapidly to 93 C. The main fraction boiled at 93 to 103 C. The conversion of 1,1,2-trimethoxyethane to crude dimethoxyethylene was 77.4%, and the yield, based on the quantity of 1,1,2-tr1methoxyethane consumed was 88.4%. The dimethoxyethylenemethanol azeotrope, boiling at 63 to 64 C. was found to have the composition 10% dimethoxyethylene and 90% methanol. Careful fractionation of the main fraction boiling at 93 to 103 C. resulted in pure 1,2-dimethoxyethylene boiling at 102 with a refractive index of 1.4190 at 25 C. (D line). 1,2-Dimethoxyethylene was identified by hydrogenation to 1,2 dimethoxyethane with Raney nickel catalyst at to C. During the purification by careful distillation (to separate the cis and trans isomers), material boiling at 97 to 985, refractive index 1.4121 at 25 (D line) was collected which evidently contained a predominating amount of one of the isomers. The 102 C. boiling dimethoxyethylene evidently was the other stereoisomer.

Example 2.1,1,2-trimethoxyethane was vaporized and passed over'a Na2B407-On-SiliCa, gel catalyst maintained at a temperature of 410 to 490 0. (space velocity, 394) The condensed effluent was distilled. A small amount of metha nol was recovered and a mixture boiling from 70 to 123 C. (B. R, dimethoxyethylene, 97 to 102 C.) was obtained.

Example 3.-A run similar to the one described in Example 2 was carried out at a temperature of ca. 500 to 600 C. at a space velocity of 1200. Most of the 1,1,2-trimethoxyethane was converted to gaseous products, less than half of the starting material being converted to liquid product boiling over 'the'range of 39 to 125 'C. It was noted that the rate of permanent gas formation increased rapidly as the temperature was raised from 500 to 600 C.

Example 4.-A mixture containing 1,1,2-trimethoxyethane (0.375 mol) and methylal-methanol azeotrope (1.5 mols methyl-a1) was passed over a silica gel catalyst at a temperature of 380 to 412 C., the space velocity of the trimethoxyethane being 281 and the space velocity or the methylal being 1120. The resulting product was condensed and redistilled, yielding a methylal-methanol fraction (weight 125.5 grams, B. P. 39 to 64 C. at atmospheric pressure) and a higher boiling fraction (B. P. 415 to 69 at 113 mm. to 120 .mm.) which was largely 1,2- dimethoxyethylene. The conversion to dimethoxyethylene based upon the quantity of trimeth oxyethane charged was 70%, and the yield of dimethoxyethylene based on the weight of trimethoxyethane consumed, as estimated from the quantity of trimethoxyethane in the highest boiling fraction, was about 90%. The distillate which was collected at 51 to 55 C., under a pressure of 113 mm. to 120 mm., had a refractive index .of 1.4128 at 25 C. (methoxyl content 69.2, 68.6%; calc. 70.4% for CH3OCH=CHOCH3).

Example 5.-A mixture containing 22.5 grams 1,1,2-trimethoxyethane and 2 grams of finely powdered acid-washed clay catalyst (of the kind employed commercially-in the refining-andc-racking of petroleum), was heated at the boiling point in an apparatus equipped with a reflux condenser. The boiling was continued at atmospheric pressure for one hour, a methanol distillate being removed overheacl. The resulting product was rapidly distilled from the catalyst at reduced pressure, and the distillates were then recombined and .redistilled, yielding 2.3 grams methanol, 1.2 grams l,2--dimethoxyethylene (B. P. 51 to 60- C. at 107 mm.), 6.7 grams recovered trimethoxyethane, and 3.7 grams of higher boiling material. With 1,1,2-triethoxyethane as the starting material, a similar result is obtained, the pyrolysis product being 1,,2-diethoxyethylene.

The dimethoxyethylene obtained as above described was quite stable to heat, and was not rapidly polymerized by heating at a temperature of C. in the presence of benzoyl peroxide catalyst. It was converted to a solid polymer, however, at a temperature of 20 C., in the presence of anhydrous boron trifluoride.

The above examples are illustrative only and numerous embodiments of the invention will occur to those who are skilled in the art. For example, while it is preferred to employ relatively low molecular weight trialkoxyethanes in the practice of the invention, the higher molecular weight trial-koxyethanes may also be employed, although they tend to decompose to aldehydic substances at "the elevated temperatures required for rapid pyrolysis. Inert diluent gases may be employed to assist the conversion of the trialkoxyethanes to dialkoxyethylenes, but the use of these diluents is generally not necessary. The pyrolysis can beconducted at anyconven-ient pressure. Pressures higher than atmospheric pressure are generally neither desirable nor necessary, best results being obtained at about atmospheric pressures or at pressures only slightly above atmospheric pressure. Excellent results are also obtained at subatmospheric pressures, but, in general, the use of pressures below atmospheric pressure is not necessary.

'Ehet'erm space velocity is used herein with the meaning which has been widely accepted for many years, i. e. it is the volume of gas (corrected to 0 C., 760 mm. pressure) which is passed over .one unit volume of catalyst per hour.

The products obtained in accordance with this invention are useful as intermediates for the manufacture :of numerous organic compounds, such as glycerin, unsaturated esters, glycol .ethers, etc. They are also useful in the manufacture of resinous materials, including polymers and interpolymers. Interpolymers of 1,2-diine'thoxyethylene with vinyl compounds, dienes, etc., can be prepared, for example. These polymers :and interpolymers .are valuable as components "of :coating. compositions, molded products, etc.

Since many embodiments 0f the invention may be made without departing "from the spirit and scope thereof, it will beunderstood that I do not limit myself except :as set forth in the following claims.

.I claim:

.1. 1,2-dimethoxyethylene.

2. The isomeric form of 1;2-dimethoXyethylene having a boiling point of 102 'C. at atmospheric pressure, and arefractive index of 1.4190 at 25 C.

3. The isomeric form of 1,2-dimethoxyethylene having a boiling point of 97 to 985 C. at atmospheric .pressure, and .a refractive index of 144121 at 25 C.

A. A process for preparing 1,2-dia-lkoxyethylenes which comprisesheatingin the vapor phase 1,1,2-tnialkoxyethanes at :a temperature within the range of 300 to 450 C. whereby pyrolysis of the 1,1,2-trialkoxyethane to 1,2-dialkoxyethylene takes place, and thereafter separating the l,2-dial-koxyethylene from the resulting mixture. I

'5. A process for preparing 1,2-dimethoxyethylene which comprises heating 1,1,2-trirnethoxyethane inJ-the Ma-per vphase at a temperature within the range of .300" -to450 'C.,.-in the presence of a barium hydroxide-silica gel catalyst, whereby pyrolysis 201 l;1,2-trimethexyethane to 1,2- dimethoxyethylene takes place, and thereafter separating 1,2-'dimethoxvethylene from the resulting product. 7

6. A process for preparing 1,2-dimethoxyethylene which comprises heating in the vapor phase- 1,1,2-trimethoxyethane, in the presence of a barium hydroxide-silica gel catalyst, at a temperature withinthe rangeof 35.0 to3'75 C. whereby 1,2-dimethox; ieth-ylene is formed, and thereafter separating from the resulting mixture.

7. .A process tor preparing a 1,2-dia1koxyethyl-' ene which comprises pyrolyzing a 1,1,2-trial-' koxyethane in the presence of a solid contact absorptive catalyst at a temperature within the range .of 300 to 450 C. and thereafter separating 1,2-dialhoxyethylene :from the resulting mixture.

8. A process for preparing l,2-1dimethoxyethylene which comprises-heating at demethanolation temperature within the range of 300 to 450 C. 1,1,2-t1imethoxyethane in the presence of a solid contact absorptive catalyst and there-.

2,479,068 I a c after separating 1,2-dimethoxyethy1ene from the REFERENCES CITED resulting mixture. 7 9. The process of claim a in which the solid 5 ifig gg ffl are m the absorptive catalyst is silica gel imprcgnated with Ba(OH)z. 5 UNITED STATES PATENTS 10. The/process of claim 8 in which the solid Number Name Date absorptive catalyst is silica gel impregnated with 2 4 863 Deebel Sept 2 1947 Na2B4O7. n

11. The process of claim 8 in which the said catalyst contains silica gel. 1

WILLIAM F. GRESHAM. 

